Electrostatic charger with resuppliable corona wire



S- W. MARTIN March 3, 1970 ELECTROSTATIC CHARGER WITH RESUPPLIABLECORONA WIRE Filed May 21, 1968 INVENTOR SAMUEL W. MART/N ATTORNEY UnitedStates Patent Office 3,499,143 Patented Mar. 3, 1970 aware Filed May 21,1968, Ser. No. 730,809

Int. Cl, H01j 37/00 US. Cl. 250-495 9 Claims ABSTRACT OF THE DISCLOSURE.

' A charger for use with electrostatic copying machines in which thecorona wire is renewable or resuppliable when it becomes suflicientlydefective by reason of dirt or other foreign matter on the wire to causeunacceptably poor quality copy. There is a supply of corona wire ofindefinite length mounted on the charger for which one or more runs offresh wire can be periodically withdrawn with provision for releasablyholding the Wire under tension during periods of use.

Background of the invention In the process of electrostatic copying, asheet of copy paper having a coating of a photoconductive insulatingmaterial is passed through a corona charging device which imparts auniform electrostatic charge to the coated side of the paper. The paperis then subjected to a light patterned image or indicia on an originaldocument whereupon the electrostatic charge is dissipated in the lightnonimage areas but is retained in the darker image areas, after whichthe sheet is subjected to an aplication of electrostatically attractabletoner particles to develop the latent image lift on the paper.

Substantially the same principles are applied in the field of reusableelectrostatic copying in which the photoconductive insulating materialis a coating on a drum or plate which is grounded and on which thelatent electrostatic image is formed anddeveloped. The developed imageis then transferred to ordinary paper, and the drum or plate is cleanedand resued in the same manner to make successive copies.

' In either of the above processes, both of which are well known in theart, it is necessary to uniformly charge the photo conductor prior toexposing it to the light pattern. One preferred methodfor charging is bymeans of corona discharge from one or more very thin wires, in'the orderof 2 to 3 mils in diameter, which are stretched across the path of thephotoconductor and to which is applied a negative electric current inthe order of 6000 volts. Although the exact phenomenonis not preciselyunderstood, it is believed that this extremely high charge breaks downthe air immediately surrounding the wire into a cloud of ions whichcauses electrons to migrate from the negative wire toward either apositive wire which completes the charging circuit in the case of a twowire charger for charging photoconductive paper,or a grounded drum orplate which completes the charging circuit inthe case of a single wirecharger for charging a reusuable photoconductor The flow of electronstoward and through the photoconductor produces a uniform electrostaticcharge or negative polarity thereon.

A major drawback of the corona discharge device'is the accumulation ofdirt and other foreign matter on the negative wire in the charging unit,which is the wire facing the sensitive side of the photoconductor. It isknown that accumulations of dirt, such, for example as paper dust, spraypaint, face powder, or dry toner particles, prevents a corona effectfrom being achieved along the portion of the wire covered by the dirt,either because the dirt acts as-an effective insulator or because thedirt increases the diameter of the wire which must remain extremely thinin order to produce the corona effect. A covering of only 2 mils hasbeen found to be sufficient to prevent a corona from being producedalong a portion of the wire. The result of this is that the portion ofthe photoconductor adjacent the dirty portion of the wire is not chargedand therefore any image projected on this portion of the photoconductoris not reproduced since no toner particles will adhere to a non-chargedarea of the photoconductor.

Thus a copy made on or from a photoconductor which has been charged witha dirty corona wire may be streaked with bands of imageless areas ofvarying width depending on the length of wire portions over which coronadischarge is not achieved due to the accumulation of dirt or otherforeign matter.

It is possible to clean dirty corona wires either by a wet swab, sincemost dirt accumulations are water soluble, or by Scrapping the dirt offwith a knife. Both of these methods and particularly the latter, have anadverse elfect on the life of the wire. Also, both methods require thatthe copying machine be sufiiciently disassembled to permit removal ofthe charging device from the machine so that it can be opened to provideaccess to the wires. It is also significant to note that it is a verydelicate, time-consuming and diifcult task to rethread a charger withcorona wires in the event that one or more should break or be dislodgedduring a wire cleaning operation. Thus the solution of cleaning thecorona wires presents obvious disadvantages.

Brief summary of the invention The present invention obviates thedisadvantages of prior art corona discharge electrostatic chargers byproviding a charging device in which the corona wire is renewable orreplaceable The principles of the present invention are embodied in apreferred form of an electrostatic charger which cons sts generally of ashell member which forms a housing for a corona discharge wire whichextends longtudinally of the shell and substantially from one endthereof to the other. The shell is provided with means for mounting itbetween a pair of spaced parallel plates which constitute a frame forsupporting the several working components which make up a copyingmachine. The charger includes a bracket or housing which projects beyondone of the frame plates so-as to be accessible to'an operator of thecopying machine. A spool of corona wire of indefinite length isrotatably mounted on the bracket with releasable means to normallyconstrain the spool against rotation, and there are supporting means onthe shell which support at least one run and preferably two runs of wirein such manner that the wire can be pulled freely through the shell whenthe spool is not constrained against rotation Tensioning means isprovided on the bracket to which the free end of the wire is releasablysecured so that the wire is maintained under proper tens on at all timesexcept when it is being replaced-A suitable electrical connection isalso made to the wire through the wire supporting means so that noelectrical connections need be disconnected when it is necessary toreplace the wire after a period of use.

In this construction, when the operative portion of corona wire in thecharger accumulates sufficient dirt so as to be considered inoperativeto produce satisfactory copy, the spool constraining means is loosenedsufiicien'tly to permit rotation of the spool and the free end of isagain placed under tension.

Having briefly described the general features of the present invention,it is a principle object thereof to provide an electrostation chargingdevice for photocopy machines having novel features of construction andoperation which avoid the disadvantages of prior art charging devices.

It is another object of the present invention to provide anelectrostatic charging device for photocopy machines in which a coronadischarge wire is renewable or replaceable when necessary as determinedby the quality of copy delivered by the copying machine.

It is still another object of the present invention to provide anelectrostatic charging device for photocopy machines in which a coronadischarge wire is renewable or replaceable without removing the chargingdevice from the copying machine and without having to disassemble anypart of the charging device.

It is yet another object of the present invention to provide anelectrostatic charging device for photocopy machines in which a coronawire is renewable or replaceable without the necessity of removing theelectrical connection to the corona wire.

A feature of the present invention is the provision of an electrostaticcharging device for photocopy machines having a self contained supply ofcorona wire and means for maintaining the wire under proper tension whenthe charging device is in use.

It is a still further object of the present invention to provide anelectrostatic charging device for photocopy machines which is readilyadaptable to known copying machines Without substantial modification, iseconomical to manufacture and reliable in operation.

These and other objects and advantages of the invention will be morereadily apparent from an understanding of the following detaileddescription of a preferred embodiment of the invention when consideredin conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of a electrostatic charging deviceembodying the principles of the present invention;

FIG. 2 is a front elevation of the rear half of the electrostaticcharging device shown in FIG. 1;

FIG. 3 is a fragmentary front elevation drawn to an enlarged scale ofthe right hand end of the component shown in FIG. 2;

FIG. 4 is a sectional view taken on the line 4-4 of FIG. 3;

FIG. 5 is a sectional view taken on the line 5-5 of FIG. 3; and

FIG. 6 is a detailed view of the electrical connection taken on line 6-6of FIG. 2.

Detailed description of the invention Referring now to the drawings andparticularly to FIG. 1 thereof, an electrostatic charger 10 embodyingthe principles of the present invention is shown as being supported bythe spaced, parallel, upstanding side frame plates 12 and 14 of whichonly fragmentary portions are shown as being suflicient for the purposeof this disclosure. The charger is supported by slots 16 extendinginwardly from an edge of the plates 12 and 14 in position to lie in thepath of a sheet of copy paper 18 which is being fed along a copy paperpath generally defined by a copy paper transport means, all in a mannerwell known in the art and forming no part of the present invention.

The charger generally comprises a pair of juxtaposed charger shells 20and 22 each of which is elongate to extend between the side plates 12and 14 of the copying machine and which are generally rectangular incross section and closed on three sides, the side of each shell facinginwardly and adjacent the opposite shell being open. Each shell isprovided with a plurality of angularly disposed tabs 24 disposed on theupper or infeed side in relation to the direction of travel of the sheetof copy paper 18 which converge in said direction of feed to definea'n'eritrance slot 26 into the charger 10. Each shell also has afiangej28 (FIG. 2) disposed along the exit side of the paper passagewaythrough the charger. A string 30 of suitable material is wound aroundeach shell in a helical pattern diverging from the center of the shell,the string 30 being engaged in slots 32 between the tabs 24 tomaintainth'e string 30, in position. The wire prevents the copy paperfromentering the shells and coming in contact with the corona wire aslocated therein. 9

Each shell is provided with an end cap 34 on the oppositeopen ends, andeach end cap 34has an outwardly extending projection 36 which engageswith the slots 16 in the frame plates ,12 and 14 to support the charger1Q therein, and also to provide a convenient means and location forsecuring the ends of corona wires in a manner well known 'inthe art. Theshell 20 is conventional in all respects and therefore need not befurther described nor shown'in greater detail.

The present invention is' embodied specifically in the shell 22 whichhouses the negative corona wire which, it will be recalled from above,is the corona wire ad-' jacent the coated side of the'photoconductivepaper and is the one adversely affected by attraction and depositthereon of foreign matter.

Referring now to FIGS. 2-5, it will be seen that a generally U-shapedbracket member or housing 40 is suitably secured to projection 36;of theend cap 34 on one end of the shell22. As best seen in FIG. 4, a boss 42is formed on the bottom wall 44 of the housing 40, and another boss 46of reduced diameter extends upwardly from the boss 42, therebydefiniriga shoulder 48 between the two bosses. Both'bosses are tapped to receivea screw 50.

A spool 52 having an aperture therethrough is mounted on the upper boss46 and rests on the shoulder 48. The spool is at least as thick as theboss 46 is high, and is held on the boss 46 by means of a washer 54which bears on the upper surface of the spool 52 to lock the spoolagainst rotation when the screw 50 is tightened. The screw 50, washer 54and shoulder 48 thus define a releasable means for normally constrainingor locking the spool against rotation. It will be understood that othermeans could be provided, such as a clamp or merely friction retainingmeans. i

The spool 52 holds a supply of corona wire 56 which, as "best seen inFIGS. 2 and 3, extends from the spool 52 through an opening 58 formed inthe projection .36 of the end cap '34, and over a pulley 60 suitablymounted in the shell 22in spaced relationship with the bottom wall 62thereof. The corona wire then extends across the length of the shell 22to another pulley 64 similarly mounted adjacent the opposite end of theshell 22. The wire passes around the pulley '64 and returns to thepulley 62, thereby forming 2 runs of spaced parallel wires. From thepulley 60, the second run of wire passes through the opening 58 and theterminal end of the wire is secured to a tensioning means.

The tensioning means comprises an L-shaped lever having an aperturedcentral portion 66 pivotally mounted on the lower boss 42 coaxially withthe spool 52 and restingon the bottom wall 44 of the bracket member 40so that the spool 52 retains the lever in operative position on thebracket member 40. One leg 68 of the lever extends away from the centralportion perpendicularly to the longitudinal axis of the shell 22 andterminates in tapped head 70 which receives a screw 72. The terminal endof the wire 56 is adapted to be wound around the screw by a few turnsafter which the screw is tightened to prevent the wire from unwindingfrom the screw 72.

The other leg 74 of the lever extends toward the shell 22 and terminatesin a hook portion 76 which holds one end of a tensioning spring 78, theother end of the spring 68 being secured to a stud 80 formed on thebracket member 40. The spring 78, when in a stressed condition,

urges the lever in a clockwise direction as viewed in FIG. 3. Thetensioning device is preferably enclosed by a suitable cover member 79secured to the :bracket 40'.

A high voltage electric current is supplied to the wire 56 by means of alead 82 having a terminal 84 resting on the pulley 64, which is made ofconductive material, the pulley 64 resting on a stud 86 (see FIG. 6)formed on the bottom wall of the shell 22 and secured thereto by a screw88.

From the foregoing, it will now be understood that when either one orboth runs of the corona wire have become covered with dirt to the extentthat poor quality copy is delivered by the copying. machine, theoperator removes the cover 79 and loosens the screws 50 and 72 for thespool and terminal end of the wire respectively. He then unwinds thewire from the screw 72 and pulls off a length of wire equivalent totwice the length of the charger 10, or approximately 20 inches. Thescrew 50 is then tightened to prevent further rotation of the spool 52after which the operator takes a turn or two of wire around the screw 72and pulls on the wire in a counterclockwise direction about the screw 50in order to rotate the tensioning lever enough to place the spring 78again under tension, the tension having been relieved when the screw 50is loosened. After the spring 78 is suitably tensioned, the screw 72 istightened, the used portion of wire is cut oif, and the cover 79replaced, whereupon the charger is again ready for operation with tworuns of fresh corona wire.

It should be understood, of course, that it is optional with theoperator as to the length of wire which is pulled from the spool sinceit may not be necessary to completely replace both runs of wire in orderto remove the cause of poor quality copy.

It is apparent from the foregoing that there is provided anelectrostatic charger with resuppliable corona wire which avoids thedisadvantages of heretofore known chargers and which achieves theforegoing objects of the invention. It is to be understood that thepresent invention is not to be considered as limited to the embodimentdisclosed herein and shown in the accompanying drawings, which isintended to be merely illustrative of the best mode presentlycontemplated for carrying out the principles of the invention and whichis subject to change in size, form, arrangement and detail of parts, theinvention being intended to cover all such variations, modifications andequivalents thereof as may be deemed to be within the scope of theclaims appended hereto.

I claim:

'1. An electrostatic charging device for photocopy machines comprising(A) an elongate housing having means adjacent the opposite ends thereoffor mounting said housing in a photocopy machine, said housing having anopening therein adjacent the path of movement of a photoconductiveelement to be electrostatically charged in the photocopy machine,

(B) means mounted on said housing for storing a supply of coronadischarge wire of indefinite length,

(C) means on said housing for supporting at least one run of-said wiresubstantially between said opposite ends of said housing and adjacentthe opening in said housing,

(D) means mounted on said housing for engaging the free end of said wireand being selectively operable to normally hold the free end of saidwire in a fixed position relative to said housing and to permit movementof said wire from said storing means through said housing,

(E) tensioning means coacting with said storing means and said engagingmeans for normally maintaining said run of wire under tension, and

(F) means for connecting a power supply to said corona wire.

2. A device according to claim 1 wherein said storing means comprises aspool rotatably mounted on said housing and including means for normallyconstraining said spool against rotation.

3. A device according to claim 1 wherein said engaging means is locatedon said housing in a position accessible to an operator without removingsaid housing from the photocopy machine.

4. A device according to claim 1 wherein said means for supporting saidwire includes means for establishing an electrical circuit to said wirefrom an external source of current.

5. An electrostatic charging device for photocopy machines comprising(A) an elongate housing having means adjacent the opposite ends thereoffor mounting said housing in a photocopy machine, said housing having anopening there-in adjacent the path of movement of a photoconductiveelement to be electrostatioally charged in the photocopy tmachine,

(B) a bracket member secured to said housing in a position to beaccessible to an operator while said housing is in the photocopymachine,

(C) means on said bracket member for storing a supply of coronadischarge wire of indefinite length,

(D) means on said housing for supporting two spaced apart parallel runsof said wire substantially between said opposite ends of said housingand adjacent the opening in said housing,

(E) means mounted on said bracket member for engaging the free end ofsaid wire and being selectively operable to normally hold the free endof said wire in a fixed position relative to said housing and to permitmovement of said wire from said storing means through said housing,

(F) tensioning means mounted on said bracket means and coacting withsaid storing means and said engaging means for normally maintaining saidruns of wire under tension, and

(G) means for connecting a power supply to said corona wire.

6. A device according to claim 5 wherein said storing means comprising aspool rotatably mounted on said bracket member and including releasablemeans for normally locking said spool against rotation.

7. A device according to claim 5 wherein said means for supporting saidruns of wire comprises a pulley mounted on said housing adjacent each ofsaid opposite ends of said housing, at least one of said pulleys beingmade of electrically conductive material and being secured to saidhousing by means which permits the terminous of an electric currentsupply line to be connected thereto.

8. A device according to claim 5 wherein said engaging means comprises alever pivotally mounted on said bracke-t member and having means on oneend thereof for removably holding said wire, and said tensioning meanscomprises spring means coacting between said bracket member and anopposite end of said lever and biasing said one end of said lever in adirection to exert a pull on said wire.

9. A device according to claim 8 wherein said lever is substantiallyL-shaped and is mounted on said bracket member coaxially with said spoolbetween said spool and a wall of said bracket member whereby said spoolretains said lever in operative position on said bracket.

References Cited UNITED STATES PATENTS 2,811,135 10/1957 Hayford et al.25049.5 X 2,856,533 10/1958 Rosenthal 250-49.5

WILLIAM F. LINDQUIST, Primary Examiner US. C X.R. 317--262

